1. Field of Invention
The present invention relates to methods to manufacture an organic electroluminescent (hereinafter referred to as “organic EL”) device, organic EL devices manufactured by the above-mentioned methods, and electronic apparatuses using the above-mentioned organic EL devices.
2. Description of Related Art
Due to high brightness, self-luminescence, quick response, luminescence by a solid organic film, and being able to be driven by a DC low voltage, an organic EL display device including a plurality of organic EL elements (elements each having the structure composed of an organic light emitting layer placed between an anode and a cathode) provided correspond to respective pixels, can exhibit superior display performance and can achieve a thin and lightweight structure, and low power consumption. Therefore, organic EL display devices have been expected to replace liquid crystal display devices in future.
As a material for light emitting layers of an organic EL element, for example, a low molecular weight organic material, such as an aluminum-quinolinol complex (Alq3), and a high molecular weight organic material (hereinafter referred to as a “polymer material”), such as polyparaphenylenevinylene (PPV), may be mentioned. When a polymer material is used, a solution thereof may be applied to form a light emitting layer.
In particular, in an organic EL display device in which a great number of pixels must be formed, when light emitting layers can be formed by applying a solution containing a polymer material using an inkjet method, significant advantages from a production point of view can be obtained. That is, when an inkjet method is used, coating and patterning can be simultaneously performed, and hence patterning can be precisely performed within a short period of time.
Furthermore, since the amount of a material which is used by an ink-jet method can be minimized, the material can be efficiently used, and as a result, the manufacturing cost can be advantageously decreased.
In FIG. 12, a related art example of an organic EL display device is shown in which light emitting layers (and hole injection layer/transport layers) are formed by an inkjet method. Since this organic EL display device is an active matrix organic EL display device, a drive thin film transistor 913 is provided in each pixel.
In this organic EL display device, after an ITO thin film is formed by deposition and then patterned corresponding to the pixels to form pixel electrodes (anodes) 911 over a substrate 802 on which the thin film transistors 913 have been provided, partitions (banks) 912 are formed using an insulating layer, and a hole injection/transport layer 910a and a light emitting layer 910b are formed by an inkjet method in each of areas surrounded by the partitions. Subsequently, over the entire upper surfaces of the partitions (banks) 912 and the light emitting layers 910b, a cathode 812 is formed by a deposition method.
According to the related art example of the organic EL display device described above, the light emitting layers and the hole injection/transport layers are formed by an inkjet method which is a liquid phase process, but the formation of thin films forming the pixel electrodes (anodes) and the cathode is carried out by a deposition method. Since a deposition method is performed in a vacuum atmosphere, which is a gas phase process, the manufacturing cost thereof is high. Hence, investigation has been conducted in order to perform a liquid phase process for forming the pixel electrodes (anodes) and the cathode instead of using a deposition method.
As a liquid phase process for forming the pixel electrodes (anodes), a related art example has been known in which an ITO film is obtained by applying a solution followed by drying. In addition, as a liquid phase process for forming the cathode, a method has been reported in which a cathode is formed by an electroless plating method using silver (Ag). See for example, Y. Sakuratani et al.; Thin Solid Film 388, 256 (2001) and R. K. Kasim et al.; Chem. mater. 10, 235 (1998)
In addition, an example in which ytterbium (Yb) is used for a cathode of an organic EL element has been known. See for example, M. Stoβel et al.; Synthetic. Metals. 111–112, (2000) 19–24.
However, since silver (Ag) has a large work function, the properties (luminescent efficiency, luminance, threshold voltage, and the like) of an organic EL element using silver for a cathode have not reached the level of practical use. In addition, although an electroless plating method is a liquid phase process, compared to an inkjet method, advantages in view of production are not significant, and the properties (such as luminescent efficiency) of the organic EL element mentioned above may be degraded in some cases.